The objective of this project is to evaluate changes in plasma proteins as an early biomarker of exposure to carcinogenic aromatic amines. Two-dimensional gel electrophoresis (2DG) has been used to study the changes induced in dog plasma by the known urinary bladder carcinogens 4-aminobiphenyl (4-ABP) and 2-naphthylamine (2-NA). 3-Aminobiphenyl (3-ABP) and 1-napthylamine (I-NA), both considered to be non-carcinogenic, were used as controls. The purpose of this study was: (1) to determine whether or not the apparent deletions on plasma proteins are specific to 4-ABP; (2) to measure the time course in the suppression of the major polypeptides during dosing and their re-synthesis during a recovery period; and (3) to determine, by microsequencing directly off the gels, the biochemical identity of the affected spots. The results indicate that the suppression is limited to 4-ABP, with 3-ABP, 2-NA and 1-NA causing no discernible change in the 2DG patterns over a 12 week dosing period. The 4-ABP caused dramatic suppression of two sets of spots. One of apparent molecular weight 32.5 kD, and pI 5.8-6.0, was identified to be the B chain of haptoglobin. This spot disappears after about two weeks of treatment and recovers slowly after dosing stops. Haptoglobin functions to bind with free hemoglobin and purge it from the blood stream. Since 4-ABP causes hemolysis, the disappearance of the haptoglobin is readily explained. Among the second set of spots, a MW 65 kD, pI 6.5-6.6 peptide, disappears much faster than the haptoglobin, and recovers more quickly. The protein is about one-fifth the intensity of haptoglobin and appears to be blocked, as N-terminal microsequencing has been unsuccessful. Work is currently underway to obtain an internal sequence of this polypeptide in order to identify it.